Timeline of the Manhattan Project

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The following is a timeline of the Manhattan Project, the effort by the United States, United Kingdom, and Canada to develop the first nuclear weapons for use during World War II. The following includes a number of events prior to the official formation of the Manhattan Project as the Manhattan Engineering District (MED) in August 1942 and a number of events after the atomic bombings of Hiroshima and Nagasaki, until the MED was formally replaced by the United States Atomic Energy Commission in 1947.

Contents 1 1939 2 1940 3 1941 4 1942 5 1943 6 1944 7 1945 8 1946 9 1947 10 References 11 External links

[edit] 1939

• August 2 — Albert Einstein signs a letter authored by physicist Leo Szilard addressed to President Franklin D. Roosevelt, advising him to fund research into the possibility of using nuclear fission as a weapon in the event that Nazi Germany may also be conducting such research. He later regretted signing the letter.
• September 1 — Nazi Germany invades Poland, beginning World War II.
• October 11 — Economist Alexander Sachs meets with President Roosevelt and delivers the Einstein-Szilard letter. Roosevelt authorizes the creation of the Advisory Committee on Uranium.
• October 21 — First meeting of the Uranium Committee, headed by Lyman Briggs of the National Bureau of Standards. $6,000 is budgeted for neutron experiments.

[edit] 1940

• March — Otto Frisch and Rudolph Peierls author the Frisch-Peierls memorandum, calculating that an atomic bomb might need as little as 1 lb of enriched uranium to work.
• April 10 — MAUD Committee established by Henry Tizard to investigate feasibility of an atomic bomb
• July 1 — Responsibility for fission research is taken over by Vannevar Bush's National Defense Research Committee.
• December — Franz Simon reports to MAUD that uranium-235 can be separated using gaseous diffusion. Gives cost estimates and technical specifications. James Chadwick realizes "a nuclear bomb...is inevitable"

[edit] 1941

• February 26 — Conclusive discovery of plutonium by Glenn Seaborg and Arthur Wahl.
• March — MAUD Committee prepares interim report urging immediate action and sends it to USA. Lyman Briggs locks it in his safe and fails to tell Uranium Committee. [1]
• May 17 — A report by Arthur Compton and the National Academy of Sciences is issued which finds favorable the prospects of developing nuclear power production for military use. Vannevar Bush creates the Office of Scientific Research and Development (OSRD)
• July 15 — The MAUD Committee issues final detailed technical report on design and costs to develop a bomb. Advance copy sent to Vannevar Bush who decides to wait for official version before taking any action
• August — Mark Oliphant travels to USA to urge development of a bomb rather than power production [2]
• October 3 — Official copy of MAUD Report reaches Bush
• October 9 — Bush takes MAUD Report to Roosevelt who approves project to confirm MAUD's findings
• December 6 — Vannevar Bush holds a meeting to organize an accelerated research project, still managed by Arthur Compton. Harold Urey is assigned to develop research into gaseous diffusion as a uranium enrichment method, while Ernest O. Lawrence is assigned to investigate electromagnetic separation methods.
• December 7 — The Japanese attack Pearl Harbor. The United States issues a formal declaration of war against Japan the next day. Four days later, Nazi Germany declares war on the United States.
• December 18 — First meeting of the OSRD sponsored S-1 project, dedicated to developing fission weapons.

[edit] 1942

• July-September — Physicist Robert Oppenheimer convenes a summer conference at the University of California, Berkeley to discuss the design of a fission bomb. Edward Teller brings up the possibility of a hydrogen bomb as a major point of discussion.
• August — Creation of the Manhattan Engineering District by the Army Corps of Engineers.
• September 13 — At a meeting of the S-1 Executive Committee, it is decided that a centralized laboratory should be established to study fast neutrons, code-named "Project Y".
• September 17 — Col. Leslie Groves is assigned command of the Manhattan Engineering District. Six days later he is appointed to Brigadier General.
• September 24 — After a visit to Tennessee, Groves purchases 52,000 acres of land in Tennessee for "Site X", which will become the Oak Ridge, Tennessee laboratory and production site.
• September 26 — The Manhattan Project is given permission to use the highest wartime priority rating by the War Production Board.
• October 15 — Groves appoints Robert Oppenheimer to coordinate the scientific research of the project at the "Site Y" laboratory.
• November 16 — Groves and Oppenheimer visit Los Alamos, New Mexico and designate it as the location for "Site Y".
• December 2 — Chicago Pile-1, the first nuclear reactor goes critical at the University of Chicago under the leadership and design of Enrico Fermi.

[edit] 1943

• February 18 — Construction begins for Y-12 at Oak Ridge, Tennessee, a massive electromagnetic separation plant for enriching uranium.
• April 5-14 — Introductory lectures began at Los Alamos, later are compiled into The Los Alamos Primer.
• April 20 — The University of California becomes the formal business manager of the Los Alamos laboratory.
• August 19 — Roosevelt and Winston Churchill sign Quebec Agreement. Team of British scientists join project as a result, including Klaus Fuchs
• October 4 — Construction begins for the first reactor at Hanford Site.

[edit] 1944

• April 5 — At Los Alamos, Emilio Segrè receives the first sample of reactor-bred plutonium from Oak Ridge, and within ten days discovers that the spontaneous fission rate is too high for use in a gun-type fission weapon.
• May — Fermi at Los Alamos tests the world's third reactor, LOPO, the first aqueous homogeneous reactor, and the first fueled by enriched uranium.
• July 4 — Oppenheimer reveals Segrè's final measurements to the Los Alamos staff, and the development of the gun-type plutonium weapon "Thin Man" is abandoned. Designing a workable "implosion" design becomes top priority of the laboratory.
• July 20 — The Los Alamos organizational structure is completely changed to reflect the new priority of "implosion".
• September 2 — Peter N. Bragg, Jr. and Douglas P. Meigs, chemists on the projects, are killed, and Arnold Kramish almost killed, while attempting to clean a clog out of a uranium enrichment device as part of the pilot thermal diffusion plant at the Philadelphia Navy Yard. Two soldiers, George LeFevre and John Tompkins, also receive extensive injuries. An explosion of liquid uranium hexafluoride, which burst nearby steam pipes, which combined with the uranium hexafluoride to shower the men with the highly corrosive hydrofluoric acid. [3]
• December — A new test reactor comes on line at Los Alamos, HYPO, using uranyl nitrate in an aqueous homogeneous reactor.

[edit] 1945

• January — Gen. Thomas Farrell named Gen. Groves' deputy.
• May 7 — Nazi Germany formally surrenders to Allied powers, marking the end of World War II in Europe.
• May 10-11 — second meeting of the Target Committee, at Los Alamos, which works to finalize the list of cities on which atomic bombs may be dropped.[4]
• June 11 — Metallurgical Laboratory scientists under James Franck issue the Franck Report arguing for a demonstration of the bomb before using it against civilian targets.
• July 16 — first nuclear explosion, testing an implosion-style plutonium-based nuclear weapon, known as "the gadget", occurs during the "Trinity" test near Alamogordo, New Mexico.
• July 24 — President Harry S. Truman discloses to Soviet leader Josef Stalin that the United States has atomic weapons. Stalin feigns little surprise; he already knows this through espionage.
• August 6 — "Little Boy", a gun-type uranium-235 weapon, is used against the city of Hiroshima, Japan.
• August 9 — "Fat Man", an implosion-type plutonium weapon, is used against the city of Nagasaki, Japan.
• August 12 — The Smyth Report is released to the public, giving the first technical history of the development of the first atomic bombs.
• August 15 — Surrender of Japan to the Allied powers.
• August 21 — Harry K. Daghlian, Jr., a physicist, receives a fatal dose of radiation from a criticality accident when he accidentally dropped a tungsten carbide brick onto a plutonium bomb core. He dies on September 15.
• October 16 — Oppenheimer resigns as director of Los Alamos, is succeeded by Norris Bradbury the next day.

[edit] 1946

• May 21 — Louis Slotin, physicist, is exposed to lethal radiation when the screwdriver he used to keep separate two halves of critical mass slips. He dies on May 30.
• Summer — Operation Crossroads begins, the first postwar nuclear test series.
  • July 1 — Crossroads shot ABLE, 21 kt.
  • July 25 — Crossroads shot BAKER, 21 kt, detonated underwater.
• August 1 — President Harry S. Truman signs the Atomic Energy Act of 1946, creating the United States Atomic Energy Commission, a civilian-run agency to serve as a successor to the Manhattan Engineering District.

[edit] 1947

• January 1 — the Atomic Energy Act takes effect, and the Manhattan Project is officially turned over to the United States Atomic Energy Commission.

[edit] References

• Richard Rhodes, The Making of the Atomic Bomb (Simon and Schuster: New York, 1986).

[edit] External links

• Chronology for the origin of atomic weapons from Carey Sublette's NuclearWeaponArchive.org
• Manhattan Project Chronology from Department of Energy's The Manhattan Project: Making the Atomic Bomb